Cyclotron with focussing-defocussing system

Abstract

Cyclotron permitting a better utilization of the power when an internal target is used. According to the invention, vertical defocussing coils are arranged along a circular path across which is arranged the target. The elongated, curved coils have the effect of destroying the vertical focusing and consequently widen the beam before impact takes place with the target, so that the latter is not damaged. Application to the production of radioisotopes.

What is claimed is: 
     
       1. A cyclotron having two pole pieces occupying the two axial faces of a relatively flat, cylindrical accelerating cavity, in the centre of which is placed a charged particle source and which has means for positioning a target within said cavity, of the type in which the pole pieces have a succession of thick, spaced sectors regularly circumferentially distributed in order to define within the cavity an alternating succession of narrow air gap zones and wide air gap zones in order to ensure the vertical focussing, wherein there is also an arrangement of elongated narrow curved arcuate coils arranged in a circular manner in the vicinity of the periphery of the cavity and means for supplying electric power thereto, in order to vary to defocus the vertical focussing conditions in the vicinity of a circular path corresponding to the radial positioning of the target the coils locally strengthening the fields in the wide air gap regions and locally weakening the field in the narrow air gap regions. 
     
     
       2. A cyclotron according to claim 1, wherein each pole piece has one coil for narrow and wide air gap zone, respectively. 
     
     
       3. A cyclotron according to claim 2, wherein the coils located in a wide air gap zone are connected to the power supply means in a direction tending to locally strengthen the magnetic field in said zone and wherein the coils located in a narrow air gap zone are connected to said power supply means with a direction tending to locally weaken the magnetic field in said zone. 
     
     
       4. A cyclotron according to claim 3, wherein all the coils are connected to a single adjustable electric power supply, the winding direction of the coils located in the wide air gap zones being the opposite to that of the winding direction of the coils located in the narrow air gap zones. 
     
     
       5. A cyclotron according to claim 3, wherein all the coils located in the wide air gap zones are connected to a first adjustable electric power supply, whilst all the coils located in the narrow air gap zones are connected to a second adjustable electric power supply. 
     
     
       6. A cyclotron according to claim 4; wherein the number of ampere turns of the coils located in the wide air gap zones exceeds the number of ampere turns of the coils located in the narrow air gap zones. 
     
     
       7. A cyclotron according to claim 1; wherein the wide air gap zones are provided with projecting circular portions locally reducing the air gap in the vicinity of the aforementioned circular path and the narrow air gap zones are provided with slots locally increasing the air gap in the vicinity of the same circular path.